Various parts of a gas turbine such as a stationary vane, a moving blade, and a combustor liner used in an air craft engine or a gas turbine of an industrial appliance are exposed to high temperature conditions for a long time. Therefore, metallic materials having excellent heat resistance, for example, a Ni-based superalloy or a Co-based superalloy is used in those parts. However, parts of gas turbines made of such heat resistant alloys occasionally occur damage such as cracks and fractures caused by thermal fatigue when the parts are used for a long time under high temperature conditions and are subjected to repeated stress (e.g., by vibration).
Conventionally, when such damage is found under periodic inspection or the like, the damaged portions are repaired by brazing (for example, see Patent Reference 1: Japanese Unexamined Patent Application, First Publication, No. 2005-103641). Practically, in the braze repairing of gas turbine parts, repairing of the damaged portion is performed by preparing a repair material by mixing an Ni-based brazing material powder added with melting point lowering elements such as B and Si and alloy powder having the same or closely similar composition as the composition of the base material, filling the repair material in the damaged portion, and subjecting the damaged parts to heat treatment under a vacuum (reduced pressure) atmosphere.
Further, repair has been proposed using a brazing material in which the content of B is reduced and strengthening elements such as Mo and W are added so as to improve the creep properties of the repaired portion in the repair structure (Non Patent Reference 1: W. A. Demo, S. Ferrigno, D. Budinger, and E. Huron, Improving Repair Quality of Turbine Nozzles Using SA659 Braze Alloy, Superalloys 2000, January 9, 2000, TMS2000, pages 713-720).